The use of boilers and boiler systems is well known in the art and many different designs have been proposed such as for instance in U.S. Pat. No. 2,065,559 (Blodgett), U.S. Pat. No. 3,280,800 (Sullivan); U.S. Pat. No. 3,368,536 (Sullivan); U.S. Pat. No. 4,170,964 (Jehn et al.); or U.S. Pat. No. 4,342,286 (Pollock).
Boilers are generally used for heating fluids such as water, glycol/water mixtures, thermal fluids, etc. or for producing steam at low or high pressure. When referring to hot water or hot fluid, reference is generally made to water or fluid having a desired temperature exceeding 250 Fahrenheit (about 120 degrees Celsius). Higher temperatures can be reached in function of the fluid. Furthermore, reference is generally made to fluid since most hot fluid generators may be used for heating water but also as aforesaid for heating thermal oils and other fluids. When feedwater is injected into the boiler, the produced steam can be used to power turbines or other steam-powered engines.
Though many boiler designs are known in the art, it remains that the vast majority of these boilers requires significant amount of energy for generating the required heated fluid or steam. As such, there is a constant need to improve the energy efficiency of boilers. However, the need for more energy efficient boilers is tempered by their costs.
One often used solution to increase the energy efficiency of boilers is to add an economizer. As is known in the art, economizers are typically a heat exchanging device that heat fluids, usually but not necessarily water, up to but normally not beyond the boiling point of that fluid. An economizer is so named because it can make use of the enthalpy in fluid streams that are hot, but not hot enough to be used in a boiler, thereby recovering more useful energy and improving the boiler's efficiency.
A common application of economizers in boilers is to capture the wasted heat from boiler stack gases (flue gases) and transfer it to the boiler feedwater. This raises the temperature of the boiler feedwater, thus lowering the needed energy input, in turn reducing the firing rates to accomplish the rated boiler output.
However, economizers are generally standalone equipment, sold separately, which require labor and parts in order to be fitted to existing boiler systems. The overall additional equipment is often bulky and requires a substantial amount of space. In addition, most of the time, the additional equipment needs to be transported to the boiler site, which also raises the costs. Moreover, the equipment is also often required by industries located in geographical regions wherein specialized or skilled labor is not readily available.
In view of the foregoing, there is a need of a different approach in the use of economizers in boilers that will mitigate at least some of the shortcomings of the current approaches.